Because films don't need to be released at the exact time they are set. People didn't ask why they released 2001 in 1969. And people don't ask why they show 2001 when that was 12 years ago.
Why was Die Hard on telly the other week when its set at christmas? Why do people eat breakfast in a film that you watch in the evening? Why is it so sunny all the way through Laurence of Arabia even when I watch it in winter?

I know what you mean, some films are set at particular times of the year, but the way IM3 is scripted it harps on about it being Christmas in the way that films purposely focus on 'the holiday season' when they are released at that time to maximise revenues

Well I asked a simple question, And all I get is people being sarcastic.

I asked why a new film was released in April and within the film it was Christmas.

Not about other films being released in certain years.

Forget it!!!

The sarcasm was because it was such a pointless question. What difference does when it is set make to when its released?
Its set at Christmas. It was released in the UK in April, in the US in May, other countries throughout the summer. It'll be on blu ray in autumn and Sky by next spring. Not a single one of those things has any bearing on when the film is set and vice versa.

I asked the same question in the main Iron Man 3 thread. It's so much a Christmas film, there are all sorts of visual allusions and sight gags that specifically refer to Christmas and the way Christmas is portrayed on film. So either it was intended as a Christmas release and someone messed up, or Pearce and Black were trying (and failing) to make a specific point. It would be interesting to know what they were thinking.

I asked the same question in the main Iron Man 3 thread. It's so much a Christmas film, there are all sorts of visual allusions and sight gags that specifically refer to Christmas and the way Christmas is portrayed on film. So either it was intended as a Christmas release and someone messed up, or Pearce and Black were trying (and failing) to make a specific point. It would be interesting to know what they were thinking.

They were thinking nothing
There's no secret, no subtext. Shane Black sets his scripts at Christmas. That's it.

It was a Shane Black film. He sets a lot of his films in Winter or at Christmas. It is a trait of his. That is the sole reason for it I imagine. Nothing more. Just like JJ Abrams Loves his lens flare, Black loves WInter. Hope it helps.

Well I asked a simple question, And all I get is people being sarcastic.

Well there's an old saying; Ask a stupid question...

But surely the sarcastic responses actually answer the question. Films don't have to be released when they are set. Just because it is not uncommon for films set at Christmas to be released near Christmas, it doesn't mean they have to be.

Why was it set at Christmas? Because that's when the writer decided to set it. Why was it released in Spring? Because that's when the studio decided to release it.